1. Field
The present embodiments relate to a lifting unit and to a patient support device.
2. Related Art
Medical diagnostics and therapy devices generally include a lifting or telescopic apparatus that adjusts equipment components. Equipment components that are commonly adjusted are, for example, X-ray emitters, X-ray detectors, object tables in mammography, C-arcs, operating tables or patient support apparatuses for C-arcs, computer tomography equipment, magnetic resonance equipment or nuclear medicine and radiation therapy equipment. Radiation, electromagnetic waves or sound waves can be used to examine or treat patients in such devices. For example, X-, electron, or particle rays, ultrasonic waves or magnetic fields can be used for treatment. Generally, the devices include relatively heavy (massive) radiation or active sources and heavy detectors. These devices are positioned in space with corresponding massive mechanical structures. The ability to position this massive mechanical structure in three dimensions is limited by the size of the structure.
Depending on the type of the examination or treatment to be carried out, the diagnostic and/or therapeutic device (termed simply DT device below) and/or its active source are brought into a specific spatial orientation and position with reference to the patient to be examined. The setting of the required spatial configuration requires devices that can be positioned in space. However, because of the generally restricted positioning ability, not every desired spatial configuration of patient and device can be produced. Depending on the type of examination or treatment, it may be necessary to position the patient in a specific way, for example, lying supine or on the side, head over heels or standing. A patient support apparatus has been conventionally used to position the patient with reference to the device. The simultaneous positioning ability of the device and of the patient increases the multiplicity of possible spatial configurations.
A patient support apparatus has one- or two-dimensional displacement in a geodetic, horizontal plane. Patient support tables generally have a patient support (table plate) that is supported in a floating fashion. The patient support may be constructed with or without linear guidance such that the patient support can be adjusted in terms of one dimension or two dimensions. In addition, the patient support can be adjusted in the height direction. Generally, a lifting device that is oriented in a geodetically vertical direction is used to raise or lower the patient support, for example, from below the patient support. The lifting apparatus can include a hydraulic, pneumatic or electric motor drive unit and have a scissor parallelogram mechanism or spindle drive mechanism. The patient support can be tilted or canted. The ability to freely position the patient support, and thus the patient, is achieved by combining all the possibilities of adjustment.
In medical practice, the ability to access the patient with as little hindrance and as freely as possible is of great value. In the course of treatment or examination, medical or technical experts should be able to approach the patient at any time. The patient support apparatus includes a supporting foot that supports the patient, is as slim as possible, and takes up little space. Depending on the patient's position, the centroid of a recumbent patient is not always situated above the supporting foot. The torque on the supporting foot is adversely affected when a patient is not positioned centrally over the supporting foot. If the patient support is displaced horizontally, this torque increases because the lever is longer. Conventionally, the supporting foot design presents a compromise between the smallest possible overall size and high stability.
A lifting apparatus for height adjustment is generally disposed in the supporting foot of the height-adjustable patient support apparatus. The lifting apparatus is subjected to the torque loading described. The torque from a patient who is not centrally recumbent leads, for example, to the vertically oriented lifting apparatus being subject to rotational and shear loads. This loading creates alignment errors in drive components that must be aligned vertically. This can apply, for example, when a hydraulic apparatus having hydraulic cylinders and pistons has a spindle drive with a spindle and nut.
A hydraulic apparatus normally has relatively large lateral guidance forces, and counteracts alignment errors by itself. However, spindle drives are vulnerable to the described problem of alignment errors. For example, a scissor mechanism or double scissor mechanism that is driven by a spindle drive has been used to adjust the height of the patient support. The scissor mechanism or double scissor mechanism is typically connected to a base plate of the patient support apparatus with a fixed bearing. The spindle of the spindle drive forms with a drive motor a structural unit that is permanently connected to the base plate. The spindle is oriented vertically when the structural unit of spindle and drive unit is connected to the base plate. The spindle nut is aligned with the spindle on the scissor mechanism or double scissor mechanism. Conventionally, if a patient who is not recumbent in a centered fashion is loaded on the patient support, the torque causes the scissor mechanism or double scissor mechanism to depart slightly from its originally vertical orientation through elastic deformation. The spindle nut is also deflected out of its position or alignment and is no longer in alignment with the spindle.
Similar problems arise when positioning devices other than patient support tables. For example, a C-arc is generally rotated on two axes, but can be moved vertically and horizontally. The considerable weight of the C-arc and the holder, which is typically on the side of the support, creates torques that deflects the vertical drive and the horizontal drive out of alignment.
The spindle nut has been made of relatively soft material, for example, plastic or bronze to counteract the problem of alignment errors between the spindle and the spindle nut and to provide a certain amount of play between the spindle and the spindle nut. The play between the spindle and the spindle nut allows the spindle drive to be operated reliably despite the occurrence of slight alignment errors. However, this increases both friction and wear between the spindle and the spindle nut.